Liquid developer for electrophotography

ABSTRACT

A LIQUID DEVELOPER FOR ELECTROHPTOGRAPHY COMPRISING A CARRIER LIQUID AND A TONER DISPERSED IN SAID CARRIER LIQUID, SAID TONER CONSISTING SUBSTANTIALLY OF FINELY-DIVIDED PARTICLES HAVING A DEFINITE COLOR, AT LEAST ONE COATING AGENT AS COATED ON THE SURFACES OF SAID PARTICLES AND SELECTED FROM THE GROUP CONSISTING OF A SYNTHETIC RUBBER, A NATURAL RUBBER, POLYCONDENSATES OF SAID TWO RUBBERS AND VINYL POLYMERS HAVING AN INSOLUBILITY AGAINST SAID CARRIER LIQUID, AND A GRAFT-POLYMER HAVING AN AFFINITY WITH SAID CARRIER LIQUID AND CONSISTING OF AT LEAST ONE VINYL MONOMER SELECTED FROM THE GROUP CONSISTING OF POLYMERIC VINYL MONOMERS, SAID GRAFT-POLYMER BEING GRAFT-COPOLYMERIZED TO SAID COATING AGENT.

United States Patent US. Cl. 252--62.1 3 Claims ABSTRACT OF THEDISCLOSURE A liquid developer for electrophotography comprising acarrier liquid and a toner dispersed in said carrier liquid, said tonerconsisting substantially of finely-divided particles having a definitecolor, at least one coating agent as coated on the surfaces of saidparticles and selected from the group consisting of a synthetic rubber,a natural rubber, polycondensates of said two rubbers and vinyl polymershaving an insolubility against said carrier liquid, and a graft-polymerhaving an affinity with said carrier liquid and consisting of at leastone vinyl monomer selected from the group consisting of polymeric vinylmonomers, said graft-polymer being graft-copolymerized to said coatingagent.

BACKGROUND OF THE INVENTION (a) Field of the invention The presentinvention relates to a liquid developer for use in developing anelectrostatic latent image formed on an image-recording material bymeans of electrostatic charge. More particularly, the present inventionrelates to a liquid developer for use in developing said image in asingle color and a set of liquid developers for use in developing saidimage in plural colors (or natural colors).

(b) Description of the prior art A well-known method in the prior art isthe so-called Wet-process developing method which comprises the steps of(1) forming a latent image 'by electrostatic charge on animage-recording material such as a highly insulating plastic film or anelectrophotographic copying material prepared by binding photoconductivepowder onto the surface of a supporting sheet such as paper, a film, ametal sheet, etc. by means of a highly insulating resin, and then (2)dipping said image-recording material carrying the thus formed latentimage in a developer prepared by dispersing electrostatically chargedpigment particles in a liquid having a high electrical resistivity,thereby developing said latent image. As the electrostatically chargedpigment particles, viz., the toner, one prepared by kneading carbonblack with a natural rosin, an asphalt or a synthetic alkyd resin addedthereto, thereby coating the former with the latter, is popular, whileas the liquid having a high electrical resistivity, viz., the carrierliquid, a parafiinic hydrocarbon having an electrical resistivity morethan 0 cm. and a dielectric constant less than 3 has hitherto beenrecommended. However, a liquid developer prepared by combining a tonerand a carrier liquid as described above has been accompanied by suchdrawbacks that, in case of prolonged preservation or repeated usethereof, the coating agent is disengaged and separated from the pigmentparticles constituting the toner to elfuse into the carrier liquid and,as a result, the toner fails to show a distinct electrification anddispersibility and finally presents a precipitation phenomenon, therebyhampering the completion of satisfactory developing.

Meanwhile, according to the currently popular copying Patented Apr. 18,1972 process employing liquid developers for plural-color(natural-color) electrophotography, a method has been adopted in whichreproduction of the images and colors of an original is performed byrepeating, say, three to four times or more often, an operationcomprising the steps that, after impression of an electric charge on acopying material having a photoconductive layer by means of coronadischarge, a colored original and a filter capable of selectivelytransmitting a desired color of said original image are superposed ontothe thus processed copying material to effect exposure therethrough,whereupon the toner having said desired color is adsorbed onto theelectrostatic latent image area formed as above. (The adsorption isusually effected by dipping said copying material in a liquiddeveloper.) However, employment of such method in reproducing aplurality of colors onto the photoconductive layer of one and the samecopying material has been accompanied by such a drawback that the toner(color) first adsorbed or adhered onto said photoconductive layer willeifuse or be separated from the first developed image into the seconddeveloper containing the toner to be adsorbed next. Also, it has beenaccompanied by a drawback that said effusion or separation of tonerwould give rise to undesirable phenomena such as pollution of the secondor succeeding developers, impairment of the color balance, etc.Consequently, when a colored image was formed on a copying material oran image-recording material by means of a set of developers forplural-color electrophotography consisting of a plurality of carrierliquids containing respectively toners of different colors, the colorconcentration of the first de veloped color-image area would becomelower than that of the last developed image-area, and not only therewould occur such pollution of the developers as set forth above, butalso the definition of the copied image would not be satisfactory.

Such drawbacks of the prior art are attributable to the toner containedin the developer: that is, they are attributable to the fact that thesubstance employed for the purpose of providing the pigments of suchcolors as red, blue, yellow, black, etc. with polarity-controllingproperty, dispersibility and fixability was a rosin, an asphalt, analkyd resin, or a vegetable oil. To be precise, when a pigment is coatedwith any of these substances and is dispersed in a carrier liquid, thegreater part of such coating agent applied to the pigment elfuses andthe quantity thereof adhered to the surface of the pigment is reduced soas to become very small, thereby resulting in a diminished fixability ofthe toner to the image-recording material and finally causing the toner,which was previously adhered onto the surface of said image-recordingmaterial as described above, to effuse or separate therefrom to becomepresent into the succeeding carrier liquid. Moreover, inasmuch as theforegoing developer has such a property that, when it is used repeatedlyor stored for a long time, the coating agent employed therein graduallycomes off the pigment, it would occasionally present such phenomena thatthe polarity of the toner would become indistinct or the toner wouldaggregate and to precipitate thereby making it impossible to reproducethe desired color.

In this context, the inventors have recently developed a toner preparedby directly graft-bonding the pigment and the coating agent so as toprevent the latter from coming oif the former. But, in the case of atoner thus prepared, the substance applicable as the pigment is limitedto a black material such as carbon black, Aniline Black and the likehaving a benzenoid ring, and, accordingly, though it has proved suitableas a monochromatic toner for providing black color, it has been stillimpossible to prepare toners of plural colors or a toner having variouscolors for use in developing a plural-color image. Moreover, since thequantity of the coating agent to be graft-bonded to the pigment wasstrictly dependent on the conditions of the surface of pigment it wasquite difficult to bond an ample coating agent in order to improve thefixability of the toner.

Further, said toner has also been defective in that the *kind of saidmonomer or monomers to constitute the coating is extremely limited as itis required for the monomer or monomers to be bonded to said benzenoidring and to act to provide the toner with afore-said properties (to wit,polarity-controlling property and dispersibility).

SUMMARY OF THE INVENTION The primary object of the present invention isto provide a liquid developer for use in electrostatic recording, whichcomprises a carrier liquid and a toner dispersed therein, said tonerhaving an improved composition so as to be capable of employing aplurality of pigments as well as a polarity-controlling resin. Thepresent invention has successfully overcome the defects of conventionaltoners by coating pigment particles with a coating agent which does notseparate from said particles or deteriorate in its coating efficiencywithin said carrier liquid and graftbonding a resin having apolarity-controlling effect and dispersing effect onto said coatingagent. In other Words, by composing a toner as above, not only does itbecome possible to employ a great variety of pigments as well aspolarity-controlling resins for the toner, but also the developercontaining the thus composed toner does not deteriorate in itsdeveloping efficiency even in case of repeated use and prolongedstorage.

The second object of the present invention is to provide liquiddevelopers for plural-color electrophotography comprising carrier liquidand toners of plural colors having a very strong fixability andseparately dispersed in said carrier liquid for each color.

The developer according to the present invention is applicable not onlyto an electrostatic recording material having a photoconductive layercapable of forming a latent image thereon by impressing an electriccharge and exposure as set forth above, but also to such anelectrostatic recording material which is capable of directly formingthereon an electrostatic latent image corresponding to an original imageby impressing an electric charge.

The toner according to the present invention consists of coloredparticles and a coating agent applied onto the surfaces of saidparticles together with a polymer grafted to said coating agent. Thuseach toner particle is provided with a double-layer coating around saidcolored particle. But, inasmuch as said polymer is graft-bonded to thecoating agent, it is possible to regard said double layer as a unitarylayer.

As the colored particles to be employed in the present invention, eitherinorganic substances or organic substances are suitable. All of suchcolored substances called pigments and such colored substances calleddyes are applicable. For example, as the black color particles, carbonblack Color Index (C.I.) 77266, Aniline Black C.I. No. 50440 (amanufacture of Imperial Chemical Industries Ltd., England, hereinafterreferred to as I Co.), Cyanine Black BX (a manufacture of SumitomoKagaku K.K.), Mogul A C.I. No. 77266, Elf Blacks C.I. No. 77266 andElftex CI. 77266 (manufactures of Godfrey L. Cabot, Inc., USA, ashereinafter referred to C Co.), Spilon Black (a manufacture of HodogayaChemical Industries Ltd., hereinafter referred to as H Co.), MonoliteFast Black BX CI. No. 50440 (a manufacture of I Co.), Spirit Black CI.No. 50415 (a manufacture of Orient Chemical Industries Ltd., hereinafterreferred to as Co.), etc. are applicable. As the red-color particles,Spilon Red C.I. Solvent Red 8 (a manufacture of H Co.), Spilon OrangeC.I. Solvent Orange (a manufacture of H Co.), Benzine Orange C.I. No.21110 (a manufacture of Sanyo Color Works Ltd., hereinafter referred toas S Co.), Brilliant Carmine 6B C.I. No. 15850 (a manufacture of S Co.),Scarlet KR C.I. No. 15865 (a manufacture of S Co.), Fast Red C.I. No.15865 (a manufacture of S Co.), Fast Rose 836 CI. No. 45160 (amanufacture of Dainichi Seika K.K., hereinafter referred to as D Co.),Monolite Fast Red B (a manufacture of I Co.), etc. are applicable. Asfor the yellow-color particles, Spilon Yellow C.I. Solvent Yellow 19 (amanufacture of H Co.), Benzine Yellow G NN C.I. No. 21100 (a manufactureof S Co.), Benzine Yellow 471 C.I. No. 21095 (a manufacture of D Co.),Monolite Fast Yellow IOG (a manufacture of I Co.), etc. are applicable.As for the blue-color particles, Victoria Blue C.I. Basic Blue 7 (amanufacture of H Co.), Methylene Blue CJI. Basic Blue 9 (a manufactureof H Co.), Oil Blue C.I. No. 61555 (a manufacture of 0 Co.), Alkali BlueC.I. No. 42750 (a manufacture of 0 Co.), Sky Blue (a manufacture of SCo.), Cyanine Blue FG (a manufacture of S Co.), Cyanine Blue NSG C.I.No. 74250 (a manufacture of D Co.), Lignol Blue NCB (a manufacture ofToyo Ink Industries Ltd.), Monastral Fast Blue G (a manufacture of ICo.), Vali Fast Blue C.I. No. 74350 (a manufacture of 0 Co.), etc. areapplicable. As for the green-color particles, Phthalocyanine Green LL (amanufacture of S Co.), Seika Light Green 0.1. No. 42040 (a manufactureof D Co.), Phthalocyanine Green F7G C.I. No. 74260 (a manufacture of DCo.), Chromofine Green G C.I. 74260 (a manufacture of D Co.),Phthalocyanine Green LX C.I. No. 42040 (a manufacture of S Co.), etc.are applicable. As for pigments of other colors than the foregoing,Spilon Violet C.I. Solvent Violet 2 (a manufacture of H Co.) isapplicable for a purple toner.

According to the present invention, these colored particles are coatedwith one kind or more than two kinds of coating agents for each color,said coating agent being selected from the group consisting of syntheticrubbers such as acrylic rubber copolymer of styrene-butadiene, PlioliteVTL or VTAL rubbers (-vinyltoluene/butadiene rubbers), butylene rubberand styrene rubber, varieties of natural rubbers such as naturalrubber-1135X (Malaya), Lacentex (Malaya), Minotex (Cambodia), Dunlop(Malaya) and RCMA (Indonesia), polycondensates of said synthetic andnatural rubbers, and polymers comprising at least one member of thegroup consisting of monomers to be expressed by the following generalFormula 1.

The properties of the above natural rubbers are described in the Oct.20, 1962 issue of Kobunshi (High Molecules) published by Kobunshi Gakkai(Society of High Molecules).

General Formula 1 H H 5:6 l

wherein, Y represents a radical selected from the group consisting ofCOOH, -H and -Cl; and X represents a radical selected from the groupconsisting of n 2n+1 n 2n+1 OC H (151154), CN, -COOH, Cl, COC1, COOR[wherein, R represents a radical selected from the group consisting of CH (15,154),

CH2CH CHg, CZH4OH, -NHCOCH3 and n 2n+l [wherein, L represents a radicalselected from the group consisting of -CH NO -NH N(CH COOH, COOCHg,--OH, OCH;,, Cl and -Br],

(wherein L is identical with said L),

(wherein, L is identical with said L, and 'n.=1-4) and -(CH2)n (wherein,L is identical with said L, and n 1-4).

Any of these coating agents is insoluble in the carrier liquid for thedeveloper as referred to later and, not only that, has such a propertythat it is easily graft-bonded to the below-mentioned monomers.Subsequent to being coated with such coating agent, the coloredfinely-divided particles are next graft-bonded respectively with such amonomer capable of forming a copolymer having an affinity With thecarrier liquid and a solubility therein. As the monomer to begraft-bonded to said particles, it is selected from the group consistingof polymeric vinyl compounds and at least one member selected from thegroup consisting of such vinyl compounds as expressed by the followinggeneral Formula 2.

General Formula 2 wherein, R represents a radical selected from thegroup consisting of H and CH and R represents a radical selected fromthe group consisting of alkyl radicals having 5 to 20 carbon atoms,cyclohexyl radical, -OR" (wherein R is identical With said radical R)and COOR (wherein R' represents a radical selected from the groupconsisting of alkyl radicals having 5 to 20 carbon atoms and cyclohexylradical).

To give concrete examples of the compound expressed by said generalFormula 2, there are enumerated such substances as vinyl stearate, vinyllaurate, vinyl oleate, tridecyl methacrylate, vinyl cyclohexylate,cyclohexyl acrylate, hexyl acrylate, heptacyl acrylate, dodecylacrylate, octyl acrylate, stearyl acrylate, tridecyl acrylate, hexadecylacrylate, n-amyl methacrylate, 2-ethylhexyl methacrylate, dodecylmethacrylate, heptadecyl methacrylate, hexyl methacrylate, stearylmethacrylate, lauryl vinyl ether, n-octyl vinyl ether, tridecyl vinylether, etc.

As the carrier liquid for the developer according to the presentinvention, any of the liquids containing liquid hydrocarbon of normalparafiin family, isoparaflin family, olefin family and naphtha family orsaid liquids combined with aromatic hydrocarbon, which are known ascarrier liquids, for developers to be used in conventional wet-processdeveloping method, are applicable. Said liquid hydrocarbon has anelectrical resistivity not less than 0 cm. and a dielectric constant notgreater than 3. To give examples of the hydrocarbon having suchproperties, there are such manufactures of 13880 Standard Oil Company asput on the market under tradenames of Naphtha No. 6, Solvesso 100,Isopar-H, Isopar-G and Isopar-L, and, besides, a manufacture of MobilOil Company sold under the trade-name Pgasol -ASl00. These manufacturerscan be employed either individually or in mixtures of plural kindsthereof.

The developer according to the present invention is prepared by thebelow-mentioned treatment of the abovedescribed materials. That is, saidcolored particles and coating agent are first mixed with asolvent-preferably a solvent capable of dissolving said coating agent,such as toluene, benzene, or n-hexaneand subjected to kneading, and thekneaded mixture is then either subjected to spray-drying with aspray-dryer or dried and thereafter pulverized into finely-dividedparticles having a grain-size of 15,u.. In this case, to make the mixingrate of said colored particles and coating agent to be parts by weightof the former against 100-500 parts by Weight of the latter will servefor bonding of the monomer in comparatively large quantities on theoccasion of the subsequent formation of graft-copolymers. Next, theparticles thus coated with the coating agent are mixed with the monomerto be graft-copolymerized, either in the presence of an appropriatesolvent or no solvent, together with a reaction-initiator having astrong hydrogen-absorbability, such as benzoyl peroxide or laurylperoxide, at a temperature of 100 C. or thereabout, whereby there isprepared a toner consisting of said coated particle which surface isprovided with a graft-polymer layer as chemically bonded thereon veryfirmly. Further, in case Where the reaction products brought about bythe graft-polymerization reaction is hardened, they are pulverized intofine particles having a grain size of about 15/L. The mixing rate ofsaid coated particles and monomers for causing saidgraft-copolymerization is not particularly limited, but to make saidmixing rate to be 100 parts by weight of the former against 50-500 partsby Weight of the latter will serve for effecting satisfactory provisionof polarity-controlling property as well as dispersibility for thetoner. And, the graft-polymerization reaction products are mixed in acarrier liquid having an intense affinity with the gra'ft-copolymerlayer and dispersed therein by means of a ball-mill and the like,whereby a concentrated liquid developer is prepared.

By diluting the thus prepared concentrated liquid developer with atleast one of those carrier liquids as described above, there is obtaineda liquid developer for use in developing an electrostatic latent image.Further, by diluting a concentrated liquid developer containing suchtoners prepared for each color as described above with respectivecarrier liquid, there is obtained liquid developer for plural-colordevelopment in one set of developers for four colors of black, yellow,blue and red. And, in case Where the toner for a single color isemployed, the liquid developer can be made into a liquid developer formonochromatic development.

In case of the thus prepared developer according to the presentinvention, the toner contained therein is coated with an increasedamount of graft-polymer as compared with conventional toners, and thiscoating does not come off or effuse into the carrier liquid, so that thefixability thereof is great. Therefore, in case of reproducing aplural-color image, even after repeated dipping in the developer, thetoner once fixed onto an electrostatic recording material does not comeoff into another developer. Thus, there is no fear of the color balancebeing impaired or the non-image area being stained, so that a faithfulreproduction of the plural-color image of the original can be expected.Moreover, inasmuch as the graft-polymer portion of the toner ischemically bonded directly onto the coating having an insolubilityagainst the carrier liquid, its bonding with the colored particles isfirm and its afiinity with the carrier liquid is great, and as a result,even after a prolonged storage and repeated use thereof, the toner candisplay a satisfactory dispersibility and does not show anydeterioration of the polaritycontrolling effect thereof. And, amonochromatic or polychromatic copied image formed by employing thedeveloper according to the present invention, when employed for transferonto another supporting material by means of a strong solvent, iscapable of being easily transferred, and the definition of thustransferred image is also satisfactory.

7 DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1 A mixture, preparedby kneading: Kg. Carbon black 1 Styrene-butadiene copolymer rubber 2.5Toluene 6.0

was subjected to spray-drying with a spray-dryer, wherebycopolymer-coated particles having a grain-size of about l-Sa wereprepared. To 500 g. of said particles were added 300 g. of hexylmethacrylate and 10 g. of benzoyl peroxide, and these substances weremixed with one an- Example 3 According to those manufacturing processesfor developer in Examples 1 and 2 and by applying those combinations ofmaterial as shown in the following Table I,

other at a temperature of 115120 C. for 24 hours, 15 avariety of liquiddevelopers were prepared.

TABLE I Developer Monomer or gral't- Polarity No. Colored particlesCoating agent polymerization Carrier liquid of toner 1 Victoria blue.Vinyl toluene-methyl methaerylate eopoly- Heptacylmethacrylate. Isopar GPositive n1er(n1ol ratio 8:2).

2 Phthaloeyanine. Acrylonitrile-paraehlorostyrene(mol rat1o2z8).Cyelohexyl aerylate Naphtha No. 6 Do.

3 Spirit black..." Gl(ycicllyl mgthiicrylate para-amino styrene Vinyllaurate Naphtha No.6/IsoparH=6/4. Do.

mo ratio :7

4 Spilon yellow-.. Hydrtixyl meth)acrylate 2,5-hydrxy styrene Tridecylvinyl ether IsoparH Do.

mo ratio 4:6

5 Benzine yellow Dimethylaminoethyl methacrylate-vinyl ben- Vinylcyelooctylate Naphtha No. 6/toluene=8/2 Do.

z0ate(mol ratio 5: 5).

6 Cyanine blue Aery1amide-2,4-dichlorostyreue(mol ratio 4:6)Steary1methacrylate Solvesso 100/Naphtha No. 6=6/4 Do.

thereby effecting graft-polymerization reaction. Subsequently, thegraft-reaction product was pulverized into particles having a grain sizeof about I whereby a toner was prepared. Then, to 500 g. of a carrierliquid prepared by mixing 8 parts by weight of Naphtha No. 6 with 2parts by weight of Solvesso 100, 100 g. of said toner was added, andthey were mixed with each other in a ball-mill for 24 hours. Thereafter,g. of thus prepared mixture was dispersed in 1000 m1. of Naphtha No. 6,whereby there was obtained a liquid developer containing the tonercharged positively.

A commercialized electrostatic recording paper'prepared by forming aphotoconductive layer on a supporting paper by means of binding zincoxide powder thereon with a resinous binder was first impressed withnegative charge by corona discharge, and thereafter an original having adesired image was superposed onto thus impressed recording paper toeffect exposure. When said recording paper was dipped in theabovementioned developer subsequent to exposure, there was formed aclearcut positive copied image reproducing faithfully said originalimage. Further, even in case where about 5000 sheets of the recordingpaper were developed through the same process as above by employing oneand the same developer over 12-month period, there was no trace ofdeterioration of the electrification property of the toner nor anyaggregation thereof, and it was possible to obtain copied images havingthe same definition as rendered by the developer in the initial stagesubsequent to manufacturing thereof. The image-area thus developed bythe developer according to the present invention is possessed of asplendid fixability, so that, even when rubbed with fingers, the tonerwill not come off, nor will the nonimage area become stained, either.

Example 2 A mixture, prepared by kneading: Kg. Brilliant Carmine 6B 2Styrene-butyl methacrylate copolymer (mol ratio of styrene/butylmethacrylate=l/3) 4.5

Benzene 10.0

The eificiency of any of these developers has proved to stand comparisonwith that of those developers obtained in Examples 1 and 2 above.

Example 4 The following examples pertain to the explanation of a set ofliquid developers for plural-color development wherein each toner ofblack, yellow, blue and red is dispersed in separate carrier liquid foreach color.

(a) Preparation of a developer containing black-color toner A mixture,prepared by kneading: Kg. Carbon black 1 Styrene-butadiene copolymer 3Toluene 6 was subjected to spray-drying with a spray-dryer, wherebycopolymer-coated particles having a grain-size of about l-5,u. wereprepared. To 500 g. of said particles were added 350 g. of n-amylmethacrylate, 500 g. of nhexane and 6.5 g. of benzoyl peroxide, andthese substances were mixed with one another at a temperature of 110ll5C. for 12 hours, thereby effecting graftpolymerization reaction.Subsequently, 100 g. of thus obtained graft-reaction products were addedto 500 g. of a mixed carrier liquid prepared by mixing 8 parts by weightof Naphtha No. 6 with 2 parts by weight of Solvesso 100, and they weremixed in a ball-mill for 24 hours, whereby a concentrated toner solutionwas prepared. Then, 10 g. of said toner solution were dispersed in 1000ml. of Naphtha No. 6, whereby there was obtained a liquid developercontaining black-color toner charged positively.

(b) Preparation of a developer containing yellow-color toner A mixture,prepared by kneading: Kg. Spilon Yellow 1.0 Methacrylic acid hydroxylethyl methacrylatebutyl methacrylate (mol ratio=1:0.2:5) copolymer 2.1Solvesso 100 4.0

was treated in the same way as in case of preparing the foregoingblack-color toner, whereby copolymer-coated particles having agrain-size of about 15,u were prepared. To 100 g. of saidcoated-particles were added g. of 2- ethyl hexylmethacrylate and 0.5 g.of benzoyl peroxide, and these substances were mixed with one another ata temperature of 1l5-120 C. for 8 hours, thereby effectinggraft-polymerization reaction. Subsequently, 50 g. of

thus obtained graft-reaction products were added to 400 g. of NaphthaNo. 6 and mixed with each other in a ball-mill for 16 hours, whereby aconcentrated yellow color toner solution was prepared. Then, 30 g. ofsaid toner solution were dispersed in 1000 ml. of Naphtha No. 6, wherebythere was obtained a liquid developer con taining yellow-color tonercharged positively.

(c) Preparation of a developer containing blue-color toner A mixture,prepared by kneading: Kg. Cyanine Blue NSG 0.5 Styrene-butylmethacrylate (rnol ratio=4:6)

copolymer 1.2 Toluene 1.5

was treated in the same way as in case of preparing the fore-goingblack-color toner, whereby copolymer-coated particles having agrain-size of about 1'5,u. were prepared. To 200 g. of said coatedparticles were added 30 g. of methacrylic acid, 120 g. of laurylmethacrylate and 2.5 g. of lauroyl peroxide, and these substances weremixed with one another at a temperature of 115-125 C. for 16 hours,thereby effecting graft-polymerization reaction. Subsequently, 100 g. ofthus obtained graft-reaction products and 500 g. of Naphtha No. 6 weremixed with each other in a ball-mill for 18 hours, whereby aconcentrated blue-color toner solution was prepared. Thereafter, 15 g.of said toner solution were dispersed in 1000 ml. of Naphtha No. 6,whereby there was obtained a liquid developer containing blue-colortoner charged positively. (d) Preparation of a developer containingred-color toner A mixture, prepared by kneading: Kg. Brilliant Carmine6B 1.5 Glycidyl methacrylate vinyl toluene (mol ratio :28 cooplymerToluene 1.0

was subjected to spray-drying as set forth in the foregoing, wherebycopolymer-coated particles having a grainsize of about 1-5a wereprepared. T o 200 g. of said coated particles were added 50 g. ofcyclohexyl methacrylate, 100 g. of tridecyl methacrylate, 0.6 g. oflauroyl peroxide, 0.4 g. of benzoyl peroxide and 100 g. of Naphtha No.6, and these substances were mixed with one another at a temperature of115-120 C. for 48 hours, thereby effecting graft-polymerizationreaction. Subsequently, 100 g. of thus obtained grafit-reaction productswere added to 500 g. of a mixed carrier liquid prepared by mixing 8parts by Weight of Naphtha No. 6 with 2 parts by weight of Isopar H, andthey were mixed in a ball-mill for 16 was prepared. Then, g. of saidtoner solution were dispersed in 100 ml. of Naphtha No. 6, whereby therewas obtained a liquid developer containing red-color toner chargedpositively.

By employing a set of liquid developers for plural-colorelectrophotography prepared as above and conventionally processing acommercialized electrophotographic copying paper (viz., a copying paperprepared by forming a photoconductive layer on a supporting paper bymeans of binding zinc oxide powder thereon with a resinous binder), aplural-color image was reproduced. To be precise, the photoconductivelayer of said copying paper was first impressed with negativeelectrostatic charge, and thereafter filters for green, red and bluecolors were interposed between a plural-color original and saidelectrified copying paper, whereby exposure was conducted. Thus exposedcopying paper was then dipped in the afore-said developer containing theblack-color toner, whereby the black image-area was first formed. Saidcopying paper having thus formed black image-area was impressed withelectrostatic charge, subjected to exposure through a redcolor filterinterposed between a plural-color original and said copying paper, andthen dipped in the developer containing the yellow-color toner, wherebythe yellow imagearea was formed. Subsequently, by applying successivelysuch processes that impression of electronic charge, exposure through agreen-color filter, dipping in the developer containing red-color toner,another impression of electrostatic charge, exposure through ablue-color filter, and dipping in the developer containing blue-colortoner in order, there was obtained a distinct plural-color copiedima'gereproducing said plural-color original faithfully. The plural-colorcopied-image thus reproduced would not show any coming-off of the tonereven when rubbed intensely with fingers, nor would the non-image areaget stained, either.

Further, even in case where 3000 sheets of said copying paper weredeveloped successively over l2-month period by employing a single set ofsuch developers as prepared in the present example, it was possible toreproduce pluralcolor images having such definition as by no meansinferior to that rendered by the developers in the initial stagesubsequent to manufacturing thereof.

Example 5 By applying those combinations of materials as shown in thefollowing Table II and according to those methods of preparingdevelopers in Example 4, 4 sets of liquid developers for plural-colorelectrophotography were prehours, whereby a concentrated red-color tonersolution pared.

TABLE II Materials for toner veloper Monomer for graft- Polarity No.Colored particles Coating agent polymerization Carrier liquid of tonerAniline black Orthotihlorostyrene-aerylonitrile Cycloheptacylmethacry1ate Isopar H Positive.

copo ymer. Spilon yellow Para-aminostyrene-methyl Lauryl vinyl et d0 Do1 methacrylate-butyl methacrylate.

""" Spilon red. ParamftrostyreneQ-chloroethyl n-Tetradecyl methfl ryatefl d0.. Do.

acry ate. Victoria blue Para-hydroxyl styrene-propyl n-Hexyl vinyl eth rNaphtha No. 6 Do.

methaerylate. Spirit black 2,4dimethyl styrene-N,N- 4-pentene do Do.

dimethyl acrylamide. Benzine yellow 471 2,4-dichlorostyrcne-glyeidylCyclopentecyl acrylate do Do. 2 methacrylate.

""" Spilon orange. Pera-(limethglamino-styrene- Stearyl vinyl ether.Isopar G.. Do.

acry to am Alkali blue Para-methoxystyrene-Z-chlorol octene d0 Do.

methyl acrylate, Dunlop. Spilon black l?ara-carboxylstyrene-arylaerylateVinyl oleate... Naphtha N0. 6/So1vesso (8/2) Do. Benzine yellow T G.Paraphenyllstyrene-isobutyl l-n0nene Naphtha N0. 6/S0lvesso 100 (9/1)Do.

met lacry ate. 3 Fast red Para-bromostyrene-hydroxyl Cyclopentecylacrylate Naphtha No. (i/Solvesso 100 (7/3) Do.

""" ethyl methacrylate.

Cyanine blue Para-phiinoxystyrene-vinyl 2-ethyl-hexyl acrylate Isopar HNigeuty a e. ive. Carbon black XO-550... 2,3-dinitrostyreue-vinylpholate Ootyl vinyl ether Isopar G Positive. Benzine yellow GNNOrthonitrilstyrene-acryl vinyl 3-hexene Naphtha No. fi/Solvesso 100(ti/4).. Do.

et er. 4 Scarlet KR Para-eytclohexyl styrene-vinyl Octadecylmethaorylate Naphtha No. 6 Do.

""" aceta e.

Phtl1alocyanineblue Glycidylmethacrylate-acrylic Cyclohexyl vinyl etherd0 Positive acid-styrene. (vinyl stearate). (negativ e) 1 1 Theefficiency of any of these 4 sets of developers has proved equal to thatof those developers in Example 4.

What we claim is: 1. A method for manufacturing a liquid developer foruse in electrophotography, which comprises the steps of: (a) kneadingparticles of a colored substance selected from the group consisting ofdyes and pigments, and (b) at least one coating agent selected from thegroup consisting of (i) a synthetic rubber selected from the groupconsisting of acrylic rubber, copolymers of styrene-butadiene, vinyltoluene-butadiene rubber, butylene rubber and styrene rubber, (ii)natural rubber, (iii) poly-condensates of said synthetic rubber andnatural rubber and (iv) polymers prepared by polymerizing at least onemonomer of the Formula 1 ii i i wherein, Y is selected from the groupconsisting of COOH, H and Cl; and X is selected from the groupconsisting of C,,H (152154), n 2n+1 2 n 2n+1 2 2 CN, COOH, Cl, COCl,COOR (wherein R is selected from the group consisting of C H 5 2(wherein, L is selected from the group consisting of (wherein L has thesame meaning as above), z)n

(wherein L has the same meaning as above and n: 1-4) and CH (wherein Lhas the same meaning as above and 12:1-4);

pulverizing the resultant mixture into finely divided particles coatedwith said coating agent;

mixing said fiinely divided first coated particles and a vinyl monomerof the Formula 2 R CHFJJ wherein, R is selected from the groupconsisting of H and CH and R is selected from the group consisting ofalkyl radicals having 5 to 20 carbon atoms, cyclohexyl, OR" (wherein R"has the same meaning as R) and COOR' (wherein R is selected from thegroup consisting of alkyl radicals having 5 to 20 carbon atoms);

polymerizing said monomer in the mixture thus obtained in the presenceof a reaction initiator having a strong hydrogen absorbability to formon said coated particles a second coating; pulverizing the resultantreaction product into fine particles having a grain size of about 15,u;and then dispersing said fine particles into a carrier liquid consistingof a liquid hydrocarbon having an electrical resistivity not less than10 9 cm. and a dielectric constant not greater than 3.

2. A method according to claim 1, wherein the mixing ratio of saidcolored substance and said coating agent is in the range of from to 500parts by weight of the latter per 100 parts by weight of the former.

3. A method according to claim 2, wherein the mixing ratio of saidfinely-divided particles coated with said coating agent and said monomeris in the range of from 50 to 500 parts by weight of the latter per 100parts by weight of the former.

References Cited UNITED STATES PATENTS 3,503,881 3/1970 Shinohara252-62.1 3,133,893 5/1964 Newman 252-41 3,471,439 10/1969 Bixler et al260-41 3,325,409 6/1967 Whitbread 25262.1 3,090,755 5/1963 Erchak et a1.25262.1

GEORGE F. LESMES, Primary Examiner J. P. BRAMMER, Assistant Examiner US.Cl. X.R.

961.2; l06308 M; 26041 C, 41.5 R

